Nesting async class methods / functions in JavaScript-CodePudding

so this is my code for the class and what i am trying to do with it

const getExternalDbInfo = require('./helperJS/get-external-db-info')
class ExternalDb {
    constructor(extdb_user, extdb_password, extdb_privilege, extdb_ip, extdb_port, extdb_sid) {
        this.extdb_user = extdb_user,
        this.extdb_password = extdb_password,
        this.extdb_privilege = extdb_privilege,
        this.extdb_ip = extdb_ip,
        this.extdb_port = extdb_port,
        this.extdb_sid = extdb_sid
    }
    async getDbData(){
        let data=await getExternalDbInfo(this.extdb_user, this.extdb_password, this.extdb_privilege, this.extdb_ip, 
            this.extdb_port, this.extdb_sid);
        return this;
    }
    async getTablespace(){
        console.log(  getDbData().tablespace_data)
        return  getDbData().tablespace_data

    }
}

const newDb= new ExternalDb("***");

(async function () {
    let x =await newDb.getDbData().getTablespace()
console.log(x)
})();

so i am trying to chain to the class methods (getDbData().getTablespace()) so that i don't have to call the external db more than once. but i get following error: (node:14468) UnhandledPromiseRejectionWarning: TypeError: newDb.getDbData(...).getTablespace is not a function. Is this even possible or is it something i am not understanding because i am a noob in async programming. i have tried returning {this, data} for the getDbData() method, but it didn't work

CodePudding user response：

You need to have two await calls. await will wait for the result of an expression, in this case, newDb.getDbData().getTablespace(). However, getDbData() returns a Promise, and it's trying to find a method called getTablespace on a Promise, which doesn't exist.

You can either seperate this into two lines:

let x = await newDb.getDbData();
let y = await x.getTablespace();

or you can nest your awaits:

let x = await (await newDb.getDbData()).getTablespace();

CodePudding user response：

Not sure if "nesting" is the right term here, it sounds like you are trying to call the one method from the other. The correct way to do that is

class ExternalDb {
    …
    async getDbData(){
        const data = await getExternalDbInfo(this.extdb_user, this.extdb_password, this.extdb_privilege, this.extdb_ip, this.extdb_port, this.extdb_sid);
        return data;
//             ^^^^
    }
    async getTablespace(){
        const data = await this.getDbData();
//      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        console.log(data);
        return data.tablespace_data;
    }
}

You would then not chain anything, but simply call

const x = await newDb.getTablespace();
console.log(x);